In this paper, we have investigated cross phase modulation (XPM) effect by copropagating two channels having wavelength of 1550.1 nm and 1550.4 nm with backward pumped fiber Raman amplifier (FRA). The cross phase modulation (XPM) effect has been analyzed by changing various parameters of FRA It is proposed that XPM increases with increase in input signal as well as pump signal power. XPM is also analyzed for different values of Raman fiber lengths and bit rates and we have achieved that the optimum value of bit rate for which the XPM is minimum for this channel spacing at 10 Gbps.

The effects of the pumping wavelength and their power on the gain flattening of a fiber Raman amplifier (FRA) are investigated. The multi-wavelength pumping scheme is utilized to achieve gain flatness in FRA. It is proposed that gain flatness becomes better with increase in number of pumping wavelengths applied. We have achieved flat gain with 0.27 dB fluctuation in a spectral range of 1475-1600 nm for a Raman fiber length of 10 km by using six pumps with wavelengths with in the 1385-1495 nm interval. The effect of multi-wavelength pumping scheme on gain saturation in FRA is also studied. It is proposed that gain saturation condition gets improved by using this scheme and this scheme is more useful for higher spans of Raman fiber length. Keywords—FRA, gain, pumping, WDM.

A 64 x 10 Gb/s nonreturn-to-zero wavelength division multiplexing system (WDM) for 100 GHz spaced with an efficient high gain optical amplifier is demonstrated using a fiber Raman amplifier (FRA). The WDM signals are propagated through a span comprising a single-mode fiber (96 km), a dispersion compensated fiber (16 km), and a Raman fiber (10 km). The FRA is pumped by only two pump wavelengths in the counterpropagating mode. The performance of this system is analyzed for different placements of Raman amplifier in the span, i.e., as pre, post, and both (pre and post), and it is concluded theoretically that the post configuration of the Raman amplifier is the best choice for the WDM system. With an input signal power of 0 dBm, a gain flatness of 4.4 dB with quality >11 dB is obtained across the frequency range of 188.35 to 194.65 THz without using any hybrid configuration or gain equalization technique for a transmission distance of 424 km. We present a comprehensive comparison of the performance of the WDM system by analyzing the results obtained from different configurations for different spans of fiber length. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

We have analyzed the effect of dispersion in fiber Raman amplifier (FRA) by propagating two channels together through the same backward pumped Raman fiber. We have investigated the quality factor and gain for different values of dispersion up to third order. The optimum value of second and third order dispersion has been evaluated for different channel spacing. It is observed that for a channel spacing of 50 GHz, the optimum value of dispersion (D) for a 10 km Raman fiber is 2 ps/nm/km and second order dispersion β2 is −2.551 ps2/km. The third order dispersion parameter β3 is also analyzed for different channel spacing from 50 GHz to 20 GHz and we have obtained its optimum value as −0.10967 ps3/km for both 50 GHz and 25 GHz, whereas for channel spacing of 20 GHz, the optimum value of β3 comes out to be −0.1469 ps3/km.

We analyzed the four wave mixing (FWM) effect by propagating two channels through the same backward pumped fiber Raman amplifier (FRA) with variations in FRA parameters. It is observed that FWM increases with increase in signal input power as well as pump power. The FWM effect is also analyzed for Raman constant \(({f}_{\text{ r }})\) to obtain the optimum value of \(({f}_{\text{ r }})\), and it is found that to have minimum FWM, the optimum value of Raman constant comes out to be 0.18. This Raman amplifier can be used for wavelength division multiplexed application with constant broadband gain.

We have investigated the effects of crosstalk in fiber Raman amplifiers (FRAs) by propagating signals through the Raman fiber. We have observed that quality factor reduces for lesser channel spacing. We have able to propagate the signals in two channels with spacing of 20GHz and quality factor above 25dB was obtained. The effect of signal input power and injected pump power on crosstalk and signal interference ratio (SIR) has analyzed. It is observed that the signal gain and the injected pump power should be limited to the value well below the threshold of Raman amplification to ensure small crosstalk and high SIR. The effect of Raman fiber length on crosstalk is also studied and it is observed that for high values of Raman fiber length, SIR reduces considerably.

This study has investigated the effects of crosstalk in fiber Raman amplifiers by propagating two channels simultaneously through the same Raman fiber. The quality factor reduces for higher bit rates and lesser channel spacing. The signals have been propagated in two channels at a bit-rate of 10 Gb/s with spacing of 50 GHz, and a quality factor above 35 dB is obtained. The effect of signal input power and injected pump power on crosstalk and signal interference ratio is also studied up to 40 Gb/s. It is observed that the signal gain and injected pump power should be limited to the value well below the threshold of Raman amplification to ensure small crosstalk and high signal interference ratio. The effect of Raman fiber length on crosstalk is also studied, and it is observed that for high values of Raman fiber length, signal interference ratio reduces considerably.

We investigated Raman gain spectrum and its dependence on Stoke's shift for fiber Raman amplifiers (FRAs). We determined that the Raman gain spectrum is fairly broad with a gain variation of less than 1 dB from the pump wavelength of 1440 to 1460 nm with maximum gain at 1451.2 nm, which corresponds to a Stoke's shift of 13.4 THz for the input signal source at 1550 nm. Also, the effect of both a co-propagating and counter-propagating scheme on FRAs was studied without using any booster before the Raman fiber, and it was determined that a small signal gain in the case of the counter-propagating scheme is much higher than that of the co-propagating scheme. The impact of the Raman constant (f(r)) on gain saturation is also illustrated. We have demonstrated that at high f(r) (>0.18), gain saturation conditions worsen. This suggests that higher saturation input powers can be achieved by selecting an f(r) value of 0.18 for small-signal gains of 20 dB and an input power of -20 dBm. We have numerically simulated the gain of a FRA for different Raman fiber lengths using varying pump powers. Gain saturation was observed when the input powers exceeded 5 dBm in an amplifier with a small signal gain of 20 dB, pump power of 1.2 W, and Raman fiber length of 8 km. (C) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.OE.51.1.015005]

We have investigated the Raman gain for different pump wavelengths and maximum gain is achieved for pump wavelength of 1451.2 nm for the input signal source at 1550 nm. Also the effect of both pump power and Raman fiber length on gain saturation in fiber Raman amplifiers(FRAs) was studied without using any booster before Raman fiber. We have numerically simulated the gain of a FRA for different Raman fiber lengths by varying pump powers. Saturation of the gain is observed to occur for input powers exceeding 10 dBm in an amplifier with small signal gain of 13.73 dB at pump power of 1.5 W and Raman fiber length of 12.5 km. Output powers of up to 2.14 W with pump to signal conversion efficiency of 71% are demonstrated.